Magnetic separator and magnetic separation method

ABSTRACT

A magnetic separation method and magnetic separator is disclosed including an enclosure within an electromagnetic coil surrounded by a ferromagnetic return frame including a first portion adjacent one side of the coil and covering the area enclosed by the coil and a second portion adjacent the other side of the coil and covering the area enclosed by the coil, and inlet and outlet means in the return frame for introducing and removing fluid from the enclosure.

United States Patent [72] Inventors Peter Grant Marston Glouster, Mam;John Joseph Nolan, Randolph, Mass.;

Laszlo Miklos Lontai, South Bend, Ind.

[21] Appl. No. 854,895

[22] Filed Sept. 3, 1969 [45] Patented Dec. 14, 1971 [73] AssigneeMagnetic Engineering Associates, Inc. Cambridge, Mass.

[54] MAGNETIC SEPARATOR AND MAGNETIC SEPARATION METHOD 29 Claims, 9Drawing Figs.

[52] U.S. Cl 210/42, 210/222, 210/427 [51] Int. Cl B01d 35/06 [50] Fieldof Search 210/42,

[56] References Cited UNITED STATES PATENTS 2,430,157 11/1947 Byld, Jr.209/224 X 2,784,843 3/1957 Braunlich 210/456 X 3,273,092 9/1966Hni1icka.... 335/216 3,429,439 2/1969 Weston 209/223 3,477,948 11/1969lnoue 210/223 X 3,503,504 3/1970 Bannister 209/223 OTHER REFERENCESScientific American, Vol. 212, No. 4, April, 1965 page 72 PrimaryExaminer-Reuben Friedman Assistant Examiner-T. A. Granger AIwrney-JosephS. landiorio ABSTRACT: A magnetic separation method and magneticseparator is disclosed including an enclosure within an electromagneticcoil surrounded by a ferromagnetic return frame including a firstportion adjacent one side of the coil and covering the area enclosed bythe coil and a second portion adjacent the other side of the coil andcovering the area enclosed by the coil, and inlet and outlet means inthe return frame for introducing and removing fluid from the enclosure.

PATENTEDUECIMSII $627,678

sum 1 BF 3 JOHN J /VOL A /V INVENTORS.

ATTORNEY.

PATENTEDBECMIHYI 3.621678 r 94 I22 142 96 RAW [46 FEED FEED fi TANK 7/8TIMING y H CONTROL /08 l.- 5 MAGNET MIDDLINGS t NON-MAGNETICS gSFYVPELl:x704 MAGNETICS FIG. 4. 162 FIELD ON E 764 FEED PERIOD 766 RINSE PERIODI68 FLUSH PERIOD I l l l l I l l I I O 5 1O 15 20 L Y ONECYCLE LASZLO MLONTA/ 20] PETER 6. MARSTO/V T r JOHN J NOLA/V mvsmons. 234-@@ 236 BY203 zaa W FIG. 8. H6. 9.

ATTORNEY.

MAGNETIC SEPARATOR AND MAGNETIC SEPARATION METHOD BACKGROUND OFINVENTION The invention relates to a magnetic separation method and amagnetic separator, and more particularly to the separating of materialsof different magnet susceptibility.

One method of magnetic separation involves passing a fluid containingthe higher susceptibility material and lower susceptibility material tobe separated through a canister containing a matrix of ferromagneticmaterial such as steel balls, steel wool or tacks subject to a magneticfield. The higher susceptibility materials adhere to the magneticcollection sites and the low susceptibility materials pass through thecanister. Periodically the flow of fluid to be processed may be haltedand a flushing operation initiated simultaneously with a deenergizationof the magnetic field to remove the higher susceptibility material fromthe canister. Interest in separating small particles such as colloidalor subcolloidal particles, and in separating materials having lowmagnetic susceptibility, including diamagnetic and paramagneticsubstances is increasing. With this increase comes the demand formagnetic separators having intense magnetic fields, and maximumeffective utilization thereof to make magnetic separation techniquestechnically and economically efficient for separation of materials ofminute size and low magnetic susceptibility in large flow volumeprocesses.

SUMMARY OF INVENTION It is therefore an object of this invention toprovide a magnetic separation method and a magnetic separator capable ofquickly, efficiently, and effectively separating particles of differingmagnetic properties with particle sizes as small as subcolloidal.

It is a further object of this invention to provide a magnetic separatorhaving a high-intensity magnetic field in its separation chamber toprovide therein high magnetic field gradients at a multiplicity ofcollection sites.

It is a further object of this invention to provide a magneticseparation method and a magnetic separator utilizing cryogenic orsuperconducting electromagnet coils.

It is a further object of this invention to provide a magnetic separatorhaving a highly efficient magnetic circuit and uniform flowcharacteristics in the separation chamber.

The invention may be accomplished by a magnetic separator including anelectromagnetic coil positioned within a recess in a ferromagneticreturn frame. Centered within the coil is an enclosure containing amagnetic matrix of ferromagnetic materials such as steel balls, wool, ortacks. Fluid to be processed flows into the enclosure through an inletmeans and out through an outlet means. With the coil energized, a highintensity, axial magnetic field establishes high field gradients at amultiplicity of collection sites within the matrix at which the highsusceptibility materials collect, while lower susceptibility ornonmagnetic materials pass through the enclosure. Maximum utilization ofthe available ampere turns is aided by maximizing the amount offerromagnetic material in the magnetic circuit contributing to themagnetic field in the matrix. For example, the return frame includes afirst portion covering the area enclosed by the coil and a secondportion adjacent the other side of the coil and covering the areaenclosed by the coil. The return frame may include a third portionextending about the external periphery of the coil between the first andsecond portions of the frame.

In preferred embodiments the inlet means may include an enlarged sectionwhose cross section area increases toward the enclosure and aferromagnetic plug spaced from the surface of the enlarged section toprovide a peripheral channel between the section and the plug. Theoutlet means may also be similarly constructed and the area within theperipheral channel in the enclosure is approximately the same as thearea of the enclosure outside the channel whereby more uniform axialflow to and through the enclosure is effected.

DISCLOSURE OF PREFERRED EMBODIMENT Other objects, features, andadvantages will occur from the following description of a preferredembodiment and the accompanying drawings, in which:

FIG. 1 is a cross-sectional, diagrammatic view of a cylindricallysymmetrical magnetic circuit configuration according to this inventionwith a magnet matrix having a great number of collection sites.

FIG. 2 is a diagram of one collection site in the magnetic matrix shownin FIG. I and the field gradient thereat.

FIG. 3 is a schematic diagram of the flow system of a magnetic separatorusing the magnet circuit of FIG. 1 according to this invention.

FIG. 4 is a timing chart for the flow system of FIG. 3.

FIG. 5 is a sectional diagram of a conventional coil usable in themagnetic circuit of FIG. 1.

FIG. 6 is a sectional diagram of a cryogenic or a superconducting coilwith refrigeration chamber usable in the magnetic circuit of FIG. 1.

FIG. 7 is a schematic sectional diagram of a coil showingregionalization of the conductors.

FIG. 8 is a sectional diagram of the arrangement of the superconductorsand normal conductors in the conductors of the outer region of the coilof FIG. 7.

FIG. 9 is a sectional diagram of the arrangement of the superconductorsand normal conductors in the conductors of the inner region of the coilof FIG. 7.

The magnetic circuit configuration according to this invention mayinclude a cylindrically symmetrical soft iron return frame 10 having acoil 12 located in a central recess 14. The chamber 16 formed centrallyof coil 12 in recess 14 may be lined with a canister 18 which extendsthrough inlet 20 and outlet 22 to external connections. Inlet 20 andoutlet 22 are provided with widened inner ports 24, 26 having conicalshaped surfaces 28, 30. Located within ports 24, 26 are conical ironplugs 32, 34 attached to surfaces 28, 30 by spacers 36, 38,respectively, which establish peripheral channels 40, 42 between thoseplugs and surfaces 28, 30. The fluid to be processed flows in inlet 20through matrix 52 in canister I8 and out outlet 22. Plugs 32, 34 andsurfaces 28, 30 are shown having conical shapes, but this is notnecessary: they may have shapes resembling pyramids, hemispheres,cylinders or they may be asymmetrical and each of different shapes;further, their surfaces may be irregular. The return frame 10 and coil12 may also deviate from symmetry, cylindrical or otherwise.

Preferably, channels 40, 42 are uniform and enclose an area ofcross-sectional flow through chamber 16 between points 44, 46, and 48,50, respectively, that is equal to approximately one half the totalcross-sectional flow area of chamber 16. The volume of chamber 16 fed bychannel 40 and emptied by channel 42 is evenly divided by the peripheralchannels 40, 42 whereby more uniform axial flow is achieved.

The more intense magnetic field throughout chamber 16 and the moreuniform flow produced by the arrangement of FIG. 1 enables the use of amore dense or finer matrix 52 in chamber 16 whereby more effectiveutilization is made of the magnetic field volume provided in chamber 16.The magnetic utilization factor, i.e. the ratio of ampere turns ormagnetomotive force present at the chamber to the total ampere turnsprovided, is very high with the structure of FIG. 1. The low leakageflux and low return path magnetomotive force drop enabled by themagnetic circuit of this invention has realized a magnetic utilizationfactor greater than 0.9: more than percent of the magnetomotive forcegenerated by the coil appears across the magnetized volume at thecanister. The uniform axial flow contributes to the effective use of avery dense matrix and a fine matrix provides a very high number ofcollection sites for magnetic particles. Further, the high-intensityaxial magnetic field available throughout chamber 16 produces high fieldgradients at those sites to attract magnetic particles.

Such sites as discussed supra are depicted in FIG. 2 where collectionsites 60, 62 are shown as north N and south S magnetic poles,respectively, in a field 64 which is concentrated in their vicinity toprovide a high field gradient. A body placed in a magnetic field canbecome magnetized whereby a magnetic dipole moment is induced in it:magnetic poles are induced at the ends of the body aligned with themagnetizing field. The magnitude of the dipole moment is a function ofthe magnetic properties and geometry of the body, and also of theintensity of the applied magnetic field. In a uniform field the force oneach pole is the same and there is no net force on the body. In a fieldgradient the force exerted on the pole at the higher field is greaterthan that exerted on the other pole and there is a net force on thebody. Such bodies as would be present in the fluid flow through chamber16 are shown adhered to sites 60, 62; particles 66, and moving to thosesites, particles 68. Lower susceptibility particles 70, those of suchlow susceptibility that they are nearly unaffected by field 64, movefreely past sites 60, 62. For the smallest and most weakly magneticparticles viscous drag will limit their motion through the fluid to acollection site. Such particles will be retained in the matrix if theyimpinge directly on a collection site. The magnetic separator of thisinvention is particularly well suited for operation in this mode becauseof its high magnetic and hydraulic efficiency which permit uniform flowdistribution throughout a great multiplicity of small, high-gradientcollection sites in large volumes of intense magnetic field.

The magnetic circuit configuration of this invention, such as embodiedin the device of FIG. 1 contributes to the high-efiiciency,high-intensity magnetic field in chamber 16 containing canister 18 andmatrix 52. One section of return frame 10 adjacent one side of coil 12covers the coil 12 and the area enclosed by it, the other section 10"adjacent the other side of the coil 12 covers the coil 12 and the areaenclosed thereby. In this manner the field applied at the matrix 52 isoptimized both as to uniformity and high intensity. A third section 10'extending about the outer periphery of coil 12 may also be used toincrease the utilization of the available ampere turns and reduceleakage flux which is a consideration both as a safety factor and tofurther improve efficiency. In FIG. 1 section 10' is shown coextensivewith section 10 and 10" but the relationship may as well reversed, i.e.sections ll) and 10" may extend beyond coil 12 to the outer surface ofsection 10''!- The arrangement of FIG. 1 may be used in a flow systemsuch as depicted in FIG. 3 including a feed tank 80, two pumps 82, 84,four directional valves 86, 88, 90, 92, with four drive units 94, 96,98, 100, a throttling valve 102, a magnet power supply 104, and a timingcontrol 108 for passing raw feed slurry to be separated through canister18 to separate the higher susceptibility particles or fraction(s) fromthe lower susceptibility fraction(s). The two outputs are, as aconvenience, referred to respectively as the magnetics and thenonmagnetics. In addition, there may be a third output, referred to asthe middlings, whose magnetic susceptibility is between that of thehigher and lower susceptibility particles. The lower susceptibilityparticles pass through the matrix, the higher susceptibility particlesadhere to the collection sites and the middlings are loosely attached tothe sites. A flushing of the matrix with the field on producesmiddlings, while flushing the canister with the field of'f, produces thehigh-susceptibility particles. Any one or more of these three separateoutputs may be a product" desired for a particular purpose. If coil 12is a conventional water cooled coil its cooling may be performed by thesystem.

In the first part of the operation cycle, or feed period, thenonmagnetics may be produced at pipe 106. The coil 12 is energized bythe power supply 104. Raw feed is moved by pump 82 from tank 80 up pipe110 to chamber 112 between pistons 114, 116 of valve 86. From there thefeed is pumped through pipe 118 to canister 18. The speed of pump 82 isadjusted to obtain a flow-velocity in the canister that is neither sogreat that the magnetic particles 66 are stripped from collection sites60, 62, nor so low that settling of the slurry occurs. Out of canister18 the processed slurry enters chamber 120 between pistons 122, 124 ofvalve 88 and out pipe 106. During this part of the cycle, water frompipe 126 is drawn by pump 84 and delivered through chamber 128 betweenpistons 130, 132 of valve 90 through pipe 134 to cool coil 12 and thenexits from pipe 136. And water from "pipe 126 also reaches chamber 138,beyond piston 132 of valve 90, through throttling valve 102. Pipe 150connects chamber 138 to chamber 148, beyond piston 124 of valve 88.Since chamber 148 communicates only with pipe 150 during this period,there is no flow of rinse water to the canister 18.

In the second part of the cycle, or rinse period, timing control 108operates units 94, 96 to change the state of valves 86, 88. As a result,in valve 86, chamber 112 now connects pipe to pipe and chamber 142,between pistons 116 and 144, connects pipe 118 to pipe 146. in valve 88chamber 120 communicates only with pipe 106 while chamber 1 38 connectspipe to canister 18. Feed now flows from tank 80 through pump 82, pipe110, chamber 112, and pipe 140 back to tank 811. In this way the fluidis kept moving to prevent settling. Water flows through valve 102,chamber 138, pipe 150, and chamber 148 to canister 18 where it backflushes middlings into pipe 118. The coil 12 is still energized andexcessive flow velocity in the canister 18 is prevented by thethrottling valve 102. The magnetics are thus retained by the matrix.From pipe 118 the middlings flow through chamber 142 of valve 86, pipe146, chamber 152, between pistons 154 and 156 of valve 92, and out pipe158. Cooling water continues to flow through coil 12 as previously.

In the third part of the cycle, or flush period, timing control 108operates units 98 and 100 and coil 12 is deenergized. As a result, invalve 92 chamber 152 now connects pipe 146 to pipe 160 and in valve 90chamber 128 connects the output of pump 84 to line 150. The matrix incanister 18, no longer subject to the magnetic field of coil 12, is nowback flushed by water under high pressure from pump 84 through chamber128 of valve 90, through pipe 150 and chamber 148 of valve 88. The freedmagnetic particles are now driven through pipe 118, chamber 142 of valve86, pipe 146, chamber 152 of valve 92 and out pipe 160. No cooling wateris supplied to deenergized coil 12 and pump 82 continues to recirculatethe feed in tank 80. At the end of this part of the cycle the first partof the cycle or feed period begins again.

The relationship of the feed, rinse, and flush periods of the operationcycle is shown in conjunction with the coil energization time in FIG. 4.Typically in a 20-minute cycle, the field is on the first 17 minutes,line 162, the feed period lasts for the first 15 minutes, line 164, therinse period occupies the next 2 minutes, line 166, and the flush periodoccupies the last 3 minutes, line 168.

Coil 12 may be a conventional water cooled coil 12', FIG. 5, having atoroidal body with a hollow center 172 for receiving a canister. Thebody is formed of a plurality of double-wound layers 174, 176, 178, ofhollow conductor 182 having longitudinal channels 184 therein forreceiving coolant. Each such double layer begins with an inlet member186 to be connected to a source of electrical energy and to a source ofcoolant to pass through channel 184 of conductors 182, and is woundinwardly in the first layer 188 to the ID. then lapped over and woundoutwardly in the second layer 191) to the OD. finally terminating inoutlet member 192. Successive double layers are generally connected inseries to a single source of electrical energy and hydraulically inparallel to a single source of coolant, but numerous alternate hookupsare possible. Insulation 194 is provided between conductors.

Coil 12 may also be a cryogenic or a superconducting coil 12", FIG. 6.In systems, such as shown in FIG. 3, wherein cyclical operation of themagnet is contemplated, cryogenic magnetics may be preferred tosuperconductor types because of their greater efficiency in suchoperations. In the context of this patent a cryogenic coil is one whichutilizes conductor materials which exhibit a large reduction inresistivity when cooled to low temperatures. A notable example of such amaterial would be aluminum of 99.9999 percent purity which when cooledfrom room temperature to 42 Kelvin exhibits a reduction in resistance ofl0,000 to 1. Thus, the electric power required to operate a deviceutilizing such a cryogenic conductor would also be reduced by a factorof 10,000 to 1. Other high-purity materials may be used. Operatingtemperatures may be as high as 100 Kelvin. Coil 12" may includeconductors 200 of high-purity aluminum, niobium tin alloy, or niobiumtitanium alloy separated by insulation 202 and maintained at 4.2 K, orother cryogenic" temperature, in a refrigeration unit 204. Unit 204 mayinclude an insulating support 206 for coil 12" mounted in helium vessel208 which receives liquid helium or other cryogenic" coolant throughneck 210 integral with vessel 208. Vents 209 may be provided in support206 to permit flow of coolant beneath the coil 12". Suspended from neck210 is vacuum vessel 212; a radiation shield 214 may be positionedbetween vessels 208, 212. Electrical connection to coil 12" is madethrough helium boiloff cooled and properly insulated leads to reduceparasitic heat transfer. Helium boilofi is recovered from neck 210 whichmay be provided with cooling coils 216 containing a suitable coolant forutilizing the still quite low temperature of the helium boilofi' toreduce the temperature of shield 214 with lower cooling coils 218 tofurther reduce heat transfer. The same double wound layer constructionused in FIG. 5 may be used to construct the superconducting magnet ofFIG. 6.

The cryogenic or superconducting magnet represents an extremelysignificant improvement in the performance and also in the processingeconomy of the magnetic separation device. Superconductors are materialswhich when cooled to near absolute zero exhibit a transition from anormal resistive state to a superconducting state characterized by zeroresistivity. This means that there is zero or very little powergenerated by a current flowing in a superconductor. Thus,superconducting windings can maintain a magnetic field for an indefiniteperiod of time without requiring any power. It is this fact which allowsthe production of very large volumes of very high magnetic fields andfield gradients in working magnetic separation systems having lowoperating costs.

The systems described utilize superconductors whose normal tosuperconducting transition temperature is below 20 Kelvin and thereforefor convenience are operated in a bath of liquid helium at approximately4.2 Kelvin. Significant improvement may be obtained in some separationprocesses by operating at field strengths in excess of 15 Testla. Thedevice described is capable of separating magnetic particles ofsubcolloidal size having magnetic susceptibility of less than 10" cg.

Coil 12" may consist of two regions 230, 232, FIG. 7. The most economicutilization of materials can be achieved by proper selection ofsuperconducting alloys, stabilizing material, current density andmechanical design for each region. In general, the outer region 230,conductors 234, use copper stabilized niobium titanium alloys and theinner 232 (higher field) region, conductors 236, use niobium tin alloysstabilized with either copper or high-purity aluminum. Stabilization maybe achieved in the conductors 234 of outer region 230 by placing lowresistivity normal conductors 201 in intimate electrical and thermalcontact with the superconductors 203, FIG. 8, and may be achieved in theconductors 236 of inner region 232 by placing low resistivity normalconductors 201 in intimate electrical and thermal contact withsuperconductors 203, FIG. 9. Thus, if a normal region is established inthe superconductor 203 the current simply transfers into the stabilizingconductors 2 01 and shunts" around the normal region. Thecross-sectional area and heat-transfer surface of the high-conductivitynormal conductors 201 is selected so that the composite conductortemperature does not exceed the superconductor transition temperatureunder the above condition and the normal region reverts to thesuperconducting state. The superconductors 203 FIG. 8 and 9, may betwisted or otherwise positionally transposed along the direction of thecurrent flow to reduce parasitic heating associated with time changingmagnetic fields and a phenomena generally referred to as flux jumping.The regionalization technique described in connection with FIG. 7 inrelation to superconducting coils is also beneficial to use withcryogenic and conventional coils.

Other embodiments will occur to those skilled in the art and are withinthe following claims:

What is claimed is:

l. A magnetic separator including an electromagnetic coil, aferromagnetic return frame proximate to and covering said coil, anenclosure within said coil, a magnetic matrix within said enclosure,said ferromagnetic return frame including a first low-reluctancemagnetic pole section arranged transverse to the direction of fluid flowand adjacent and covering a first end of said enclosure forconcentrating at said first end the magnetic field produced by said coiland a second lowreluctance magnetic pole section arranged transverse tothe direction of fluid flow and adjacent and covering the second end ofsaid enclosure for concentrating at said second end the magnetic fieldproduced by said coil to produce a concentrated magnetic field uniformand parallel to the direction of fluid flow between said pole sectionsin said magnetic matrix, inlet means including at least one inputchannel in said first pole section to provide fluid flow through saidfirst pole section into said magnetic matrix parallel to the directionof the magnetic field in said magnetic matrix and outlet means includingat least one outlet channel in said second pole section to provide fluidflow through said second pole section from said magnetic matrix.

2. The separator of claim 1 in which said return frame includes a shellextending closely adjacent about the external periphery of said coil andinterconnecting said first and second pole sections.

3. The separator of claim 1 in which said inlet means includes a firstrecess that increases in cross section area towards said enclosure and afirst ferromagnetic plug in said first recess spaced from the surface ofsaid first recess to form a first peripheral channel and increase theferromagnetic mass of said first pole section.

4. The separator of claim 3 in which said outlet means includes a secondrecess that increases in cross section area towards said enclosure and asecond ferromagnetic plug in said second recess spaced from the surfaceof said second recess to form a second peripheral channel and increasethe ferromagnetic mass of said second pole section.

5. The separator of claim 4 in which approximately one-half of thecross-sectional area of said matrix is within the area encompassed bysaid peripheral channels.

6. The separator of claim 1 including a flow system comprising means forproviding raw material to be processed to said inlet means, means fordelivering less-magnetic particles from said outlet means to a firstoutput channel, means for providing a wash fluid to said enclosure torinse out middlings, means for delivering said middlings to a secondoutput channel, means for providing a wash fluid to said enclosure toflush out the more-magnetic particles, and means for delivering saidmore-magnetic particles to a third output channel.

7. The separator of claim 6 further including control means forsequencing operations of said flow system.

8. The separator of claim 1 in which said coil includes a plurality ofindividual segments each having a separate input and output terminalaccessible external to said coil.

9. The separator of claim 7 in which each said segment is made of aconductor having a longitudinal cooling conduit.

10. The separator of claim 8 in which said input and output terminalsinclude electrical connection means and fluid connection means forinjecting coolant into and receiving coolant from said longitudinalcooling conduits.

11. The separator of claim 1 in which said coil includes a plurality ofregions subject to different magnetic field strengths, each of saidregions containing conductors of a different material.

12. The separator of claim 11 in which said coil is a superconductingcoil.

13. The separator of claim 12 in which one of said materials is aniobium tin alloy, and another of said materials is a niobium titaniumalloy.

14. The separator of claim 1 in which said coil is a superconductingcoil.

15. The separator of claim 1 in which said coil is a cryogenic coil.

16. The separator of claim 14 further including refrigeration apparatussurrounding said coil including a vacuum vessel, a coolant vessel withsaid vacuum vessel, and a boilofi outlet pipe making said coolant vesselaccessible to an external source of refrigerant.

17. The separator of claim 16 in which said refrigeration apparatusfurther includes a radiation shield between said vacuum vessel andcoolant vessel.

18. The separator of claim 17 in which said refrigeration apparatusfurther includes cooling coils, a portion of which are proximate saidboiloff outlet pipe and a portion of which are proximate said radiationshield for conducting heat from said shield to said boiloff outlet pipeto maintain said shield at a temperature intermediate said ambienttemperature and the temperature of said superconducting coil.

19. The separator of claim 14 in which said superconductors arethermally stabilized by intimate thermal and electrical contact with ahigh conductivity nonnal conductor, the composite thereof being suitablycooled.

20. The separator of claim l9 in which said superconductors arepositionally transposed along the direction of the cu rrent flow.

21. A magnetic separator comprising:

a superconducting coil;

a ferromagnetic return frame proximate said coil including a firstportion adjacent one side of said coil and covering the area enclosed bysaid coil and a second portion adjacent the other side of said coil andcovering the area en closed by said coil;

an enclosure within said coil and return frame and within the magneticfield produced by said coil;

inlet and outlet means in said return frame for introducing andremoving, respectively, fluid from said enclosure;

refrigeration apparatus surrounding said coil including a vacuum vessel,a coolant vessel with said vacuum vessel;

a boilofi outlet pipe making said coolant vessel accessible to anexternal source of refrigerant;

a radiation shield between said vacuum vessel and coolant vessel; and

cooling coils, a portion of which are proximate said boiloff outlet pipeand a portion of which are proximate said radiation shield forconducting heat from said shield to said boiloff outlet pipe to maintainsaid shield at a temperature intermediate said ambient temperature andthe temperature of said superconducting coil.

22. A method of magnetically separating materials of different magneticsusceptibility comprising: energizing an electromagnetic coil to producea magnetic field; directing the magnetic field through the center ofsaid coil through an enclosure within the coil and a magnetic matrixwithin the enclosure; concentrating the magnetic field in first andsecond low reluctance magnetic pole sections arranged transverse to thedirection of fluid flow through said matrix and adjacent and coveringthe ends of said enclosure to produce a uniform magnetic field parallelto the direction of fluid flow through said matrix; and submitting aslurry including the materials to be separated through said magneticmatrix parallel to the concentrated magnetic field therein through inletmeans including at least one input channel in said first pole sectionand removing the slurry from said matrix through outlet means includingat least one outlet channel in said second pole section.

23. The method of claim 22 in which said magnetic field is furtherdirected through a ferromagnetic shell extending closely about theexternal periphery of said coil and interconnectin said first and secondpole sections.

24. e method of claim 22 in which said includes a first recess thatincreases in cross section area toward said enclosure and aferromagnetic plug in said first recess spaced from the surface of saidfirst recess to provide a first peripheral channel.

25. The method of claim 24 in which said by outlet means includes asecond recess that increases in cross sectional area toward saidenclosure and a second ferromagnetic plug in said second recess spacedfrom the surface of said second recess to provide a second peripheralchannel.

26. The method of claim 25 in which approximately half of the slurry isdistributed through the enclosure within the area defined by theperipheral channels.

27. The method of claim 22 further including providing raw material tobe processed to said inlet means delivering lessmagnetic particles fromsaid outlet means to a first outlet channel providing a wash fluid tosaid enclosure to rinse out middlings delivering said middlings to asecond output channel providing wash fluid to said enclosure to wash outmoremagnetic particles and delivering said more-magnetic particles to athird output channel.

28. The method of claim 22 in which said electromagnetic coil is asuperconducting coil.

29. The method of claim 22 in which said electromagnetic coil is acryogenic coil.

2. The separator of claim 1 in which said return frame includes a shellextending closely adjacent about the external periphery of said coil andinterconnecting said first and second pole sections.
 3. The separator ofclaim 1 in which said inlet means includes a first recess that increasesin cross section area towards said enclosure and a first ferromagneticplug in said first recess spaced from the surface of said first recessto form a first peripheral channel and increase the ferromagnetic massof said first pole section.
 4. The separator of claim 3 in which saidoutlet means includes a second recess that increases in cross sectionarea towards said enclosure and a second ferromagnetic plug in saidsecond recess spaced from the surface of said second recess to form asecond peripheral channel and increase the ferromagnetic mass of saidsecond pole section.
 5. The separator of claim 4 in which approximatelyone-half of the cross-sectional area of said matrix is within the areaencompassed by said peripheral channels.
 6. The separator of claim 1including a flow system comprising means for providing raw material tobe processed to said inlet means, means for delivering less-magneticparticles from said outlet means to a first output channel, means forproviding a wash fluid to said enclosure to rinse out middlings, meansfor delivering said middlings to a second output channel, means forproviding a wash fluid to said enclosure to flush out the more-magneticparticles, and means for delivering said more-magnetic particles to athird output channel.
 7. The separator of claim 6 further includingcontrol means for sequencing operations of said flow system.
 8. Theseparator of claim 1 in which said coil includes a plurality ofindividual segments each having a separate input and output terminalaccessible external to said coil.
 9. The separator of claim 7 in whicheach said segment is made of a conductor having a longitudinal coolingconduit.
 10. The separator of claim 8 in which said input and outputterminals include electrical connection means and fluid connection meansfor injecting coolant into and receiving coolant from said longitudinalcooling conduits.
 11. The separator of claim 1 in which said coilincludes a plurality of regions subject to different magnetic fieldstrengths, each of said regions containing conductors of a differentmaterial.
 12. The separator of claim 11 in which said coil is asuperconducting coil.
 13. The separator of claim 12 in which one of saidmaterials is a niobium tin alloy, and another of said materials is aniobium titanium alloy.
 14. The separator of claim 1 in which said coilis a superconducting coil.
 15. The separator of claim 1 in which saidcoil is a cryogenic coil.
 16. The separator of claim 14 furtherincluding refrigeration apparatus surrounding said coil including avacuum vessel, a coolant vessel with said vacuum vessel, and a boil-offoutlet pipe making said coolant vessel accessible to an external sourceof refrigerant.
 17. The separator of claim 16 in which saidrefrigeration apparatus further includes a radiation shield between saidvacuum vessel and coolant vessel.
 18. The separator of claim 17 in whichsaid refrigeration apparatus further includes cooling coils, a portionof which are proximate said boil-off outlet pipe and a portion of whichare proximate said radiation shield for conducting heat from said shieldto said boil-off outlet pipe to maintain said shield at a temperatureintermediate said ambient temperature and the temperature of saidsuperconducting coil.
 19. The separator of claim 14 in which saidsuperconductors are thermally stabilized by intimate Thermal andelectrical contact with a high conductivity normal conductor, thecomposite thereof being suitably cooled.
 20. The separator of claim 19in which said superconductors are positionally transposed along thedirection of the current flow.
 21. A magnetic separator comprising: asuperconducting coil; a ferromagnetic return frame proximate said coilincluding a first portion adjacent one side of said coil and coveringthe area enclosed by said coil and a second portion adjacent the otherside of said coil and covering the area enclosed by said coil; anenclosure within said coil and return frame and within the magneticfield produced by said coil; inlet and outlet means in said return framefor introducing and removing, respectively, fluid from said enclosure;refrigeration apparatus surrounding said coil including a vacuum vessel,a coolant vessel with said vacuum vessel; a boil-off outlet pipe makingsaid coolant vessel accessible to an external source of refrigerant; aradiation shield between said vacuum vessel and coolant vessel; andcooling coils, a portion of which are proximate said boil-off outletpipe and a portion of which are proximate said radiation shield forconducting heat from said shield to said boil-off outlet pipe tomaintain said shield at a temperature intermediate said ambienttemperature and the temperature of said superconducting coil.
 22. Amethod of magnetically separating materials of different magneticsusceptibility comprising: energizing an electromagnetic coil to producea magnetic field; directing the magnetic field through the center ofsaid coil through an enclosure within the coil and a magnetic matrixwithin the enclosure; concentrating the magnetic field in first andsecond low reluctance magnetic pole sections arranged transverse to thedirection of fluid flow through said matrix and adjacent and coveringthe ends of said enclosure to produce a uniform magnetic field parallelto the direction of fluid flow through said matrix; and submitting aslurry including the materials to be separated through said magneticmatrix parallel to the concentrated magnetic field therein through inletmeans including at least one input channel in said first pole sectionand removing the slurry from said matrix through outlet means includingat least one outlet channel in said second pole section.
 23. The methodof claim 22 in which said magnetic field is further directed through aferromagnetic shell extending closely about the external periphery ofsaid coil and interconnecting said first and second pole sections. 24.The method of claim 22 in which said inlet mens includes a first recessthat increases in cross section area toward said enclosure and aferromagnetic plug in said first recess spaced from the surface of saidfirst recess to provide a first peripheral channel.
 25. The method ofclaim 24 in which said by outlet means includes a second recess thatincreases in cross sectional area toward said enclosure and a secondferromagnetic plug in said second recess spaced from the surface of saidsecond recess to provide a second peripheral channel.
 26. The method ofclaim 25 in which approximately half of the slurry is distributedthrough the enclosure within the area defined by the peripheralchannels.
 27. The method of claim 22 further including providing rawmaterial to be processed to said inlet means delivering less-magneticparticles from said outlet means to a first outlet channel providing awash fluid to said enclosure to rinse out middlings delivering saidmiddlings to a second output channel providing wash fluid to saidenclosure to wash out more-magnetic particles and delivering saidmore-magnetic particles to a third output channel.
 28. The method ofclaim 22 in which said electromagnetic coil is a superconducting coil.29. The method of claim 22 in which said electromagnetic coil is acryogenic coil.